Polymeric fillers are a necessary part of the geometry of most flexible tubulars, such as umbilicals, and are used as packing, often as round, separate components disposed within the tubular. However, because most filler plastics used in the construction of umbilicals have a specific gravity of less than or equal to 1.0, it becomes costly and/or difficult to design umbilicals which meet specific weight requirements or weight-to-diameter ratios. Desired weight considerations can include suitability for dynamic and/or seabed stability, and will often result in having to add additional armor passes, which in turn increases the outer diameter (OD) of the umbilical. This adds additional cost and, more importantly, adds additional weight which in turn increases the tensile loading of the umbilical and often puts more strain on the internal core elements, resulting in larger crush forces during installation and recovery.
Current umbilical art also requires maintaining a high density in an umbilical, which may make it more stable while hanging from the platform or on the sea floor. Because many plastics comprise densities close to the density of water and because there is typically a lot of open space in an umbilical, manufactures are often forced to use a significant amount of armor, e.g. steel or other metal, on the umbilical to increase its density. However, as the amount of armor needed for density is increased, the total amount of armor also rises to be able to hold up the weight of the umbilical, resulting in a larger umbilical larger. When the umbilical is installed, this extra weight may present a significant load and the deploying mechanism, e.g. a vessel, has to apply a large crush tension (normal force) to keep the umbilical from slipping through the deploying device. This crush load may be high and damage interior core elements such as hoses, reducing the lifespan of the umbilical and its core components.
Accordingly, current art typically uses polymeric fillers as packing around internal components. These internal components may be stranded together in a helix and a layer of polymeric fillers such as polyethylene extruded over them; the components may then be stranded, often in an S-Z pattern over an internal core. An extruded sheath is then disposed over the bundled components with armor such as steel rods stranded over the outside, e.g. helically. Finally, another sheath is extruded over the armor. This design has shortcomings. For example, a high density in the umbilical is required, making it more stable while hanging from the platform or on the sea floor because the plastic used is very close to the density of water and there is a lot of open space in the umbilical. This, in turn, requires use of a lot of armor on the umbilical to increase its density but as the amount of armor increases for density an even greater amount of armor is required to be able to hold up the weight of the umbilical, making the umbilical larger. Another shortcoming is that an umbilical being installed is often gripped by a tensioner while up to 2500 m of umbilical are hanging off the end of the vessel. This is a significant load for the cable and the vessel has to apply a large crush tension (normal force) to keep the umbilical from slipping through the tensioner. This crush load can damage internal umbilical components such as hoses and reduces the lifespan of those components.